This study addresses narcotic analgesic-induced euphoria using two morphine self-dosing paradigms. The first involves postoperative patients using patient-controlled analgesic therapy (PCA), an established method of controlling pain whereby patients are allowed to self-administer intravenous narcotic analgesics via a timing sequencer device. The second trial involves postaddicts who will self-administer morphine in a similar environment and contorl. Both trials will evaluate subject sedation and euphoria status in addition to determining free morphine and endorphin concentrations in plasma. Comparisons will be made between groups in an attempt to delineate use (self-dosing to eradicate pain) and abuse (self-dosing in a pain-free subject dosing to euphoria). Among the analyses to be applied will be correlations between sensorium and endorphin and/or morphine levels; correlations between endorphin and morphine levels; comparisons of diurnal and other dosing patterns; approximations of target plasma concentrations (if possible); pain versus sedation versus euphoria histograms; sedation versus euphoria versus frequency histograms; evaluation of physiologic monitoring parameters; and comparisons of morphine clearance estimates. Results will provide insight into 1) PCA use and abuse, 2) sensorium character delineations of narcotic use versus misuse, 3) plasma morphine and endorphin level relationships, 4) differences between postaddicts and patients in morphine clearance, plasma endorphin levels and relationships thereof, and 5) succinct criteria for differentiating use versus abuse of PCA. Results will undoubtedly open new doors with questions for further research, as this proposal is the first application of PCA in this area.